# Copyright 2021 Zilliz. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


import threading
from functools import wraps


def singleton(cls):
    """
    Wrapper that creates singleton instance of class that it is fed.

    Returns:
        any: Singleton instance of class.
    """
    instances = {}
    lock = threading.Lock()

    @wraps(cls)
    def wrapper(*args, **kargv):
        if cls not in instances:
            with lock:
                if cls not in instances:
                    instances[cls] = cls(*args, **kargv)
        return instances[cls]
    return wrapper
